The present invention relates to a metal gasket such as a cylinder head gasket to be installed between two engine members, such as a cylinder head and a cylinder block of an internal-combustion engine, to seal therebetween.
When joint surfaces of the cylinder head and the cylinder block (cylinder body) of an automobile engine are sealed, a metal cylinder head gasket is installed between the cylinder head and cylinder block, so that combustion gas, coolant water, or lubricating oil can be sealed.
Due to demands for a lighter engine, manufacturing cost reduction, and so on, the cylinder head gasket has being shifted to a gasket with a simple structure formed by one or two metal substrates or plates from a laminated type wherein a number of metal substrates are laminated. Accordingly, since the substrates are formed by one or two plates, and also usable materials are limited due to the lighter engine, the type and quantity of sealing means are also limited, so that there is no choice but to use a relatively simplified sealing means.
On the other hand, even if the cylinder head gasket seals between the engine members, there is a large difference in the sealing performance required according to type of sealing-target holes. Accordingly, in a cylinder bore, it is necessary to seal high-heat and high-pressure combustion gas in a cylinder. On the other hand, in a liquid hole for circulating coolant water or engine oil, it is necessary to seal relatively low-heat and low-pressure liquid.
Also, due to an engine structure, there is a difference of the surface pressure around the cylinder bore surrounded by bolt holes for tightening bolts; and the liquid hole located outside the bolt hole in many cases, wherein a pressure bonding force by the tightening bolt acts in only one side.
Especially, high surface pressure is required around the cylinder bore. However, the engine members made from a relatively soft aluminum alloy are required not to be damaged, so that it is difficult to use a metal substrate with high stiffness. As a result, there is a problem that the shape and arrangement of a conventional bead cannot provide enough stiffness.
In the above-mentioned cylinder head gasket, when a bead is simply provided, the stiffness and sealing performance of the bead depend on the shape of the bead and the material characteristic or thickness of the metal substrate. Accordingly, this reduces the possibility of design, and leads to the difficulty in having an appropriate sealing performance respectively relative to each sealing-target hole.
Specifically, in order to improve the stiffness of the bead, the plate thickness, plate material, and the bead structure such as the curvature and height of the bead are required to be changed. However, in an actual gasket design, overall optimization is required so that changes of the plate thickness and material are not easy. In the above-mentioned condition, a gasket capable of locally improving the stiffness or following-up of the bead is required.
Therefore, as shown in FIG. 8, a gasket 2 was proposed mainly as the cylinder head gasket (e.g. refer to the Patent Document 1). In the gasket 2, a main bead 6A and sub-beads 6B linearly connecting to the bottom portions of the main bead 6A are formed in a metal substrate 2, and the surface pressure is generated intensively on the top portions of the main bead 6A and the sub-beads 6B, so that the gasket 2 can be reliably sealed with large surface pressure.
However, due to frictional force generated on the top portions of the sub-bead 6B, the bottom portions of the main bead 6A are prevented from enlarging to some expansion, and improve the stiffness of the main bead 6A, so that relatively large sealing surface pressure can be obtained. However, there is a limitation to stop the expansion of the top portions of the sub-beads 6B only by the frictional force, so that it is not enough to obtain large stiffness.
Also, as shown in FIG. 9, as a metal gasket constituted by two structures, the following metal gasket is proposed. Although the sealing subjects are holes for an engine intake-exhaust system, cross-sectional shapes of circular beads 4 elastically surrounding the holes 2 project in the opposite directions, respectively, from flat parts of metal substrates 1. Also, two plates are formed to have waves with two mountain-shaped portions 4a, 4b which are continuing each other, and are laminated such that both tops of the mountain-shaped portions 4a of the circular beads 4 abut each other. One metal plate provides a circular bead 4 with a crushed amount of two heights of the mountain-shaped portions, and allows the circular bead 4 to adequately elastically deform. As a result, the metal gasket prevents leakage of the medium which should be sealed more effectively (for example, refer to the Patent Document 2). Incidentally, reference number 3 in FIG. 9 indicates a bolt hole.
However, in the gasket with the two structures wherein the wavelike and mountain-shaped top portions 4a abut against each other, when the abutting beads 4 slip, compressive stiffness of the beads 4 does not reach predetermined compressive stiffness, so that an intended effect cannot be obtained. As a result, the abutting beads 4 are required to be positioned with a high degree of accuracy. Since the positioning requires an advanced technique, it is difficult in a practical point for the cylinder head gasket with a structure including a minute bead whose width is 3 mm and below.
Patent Reference 1: Japanese Patent Publication No. H11-230355 (FIG. 2, page 2)
Patent Reference 2: Japanese Patent Publication No. 2002-54502 (FIG. 2, page 3)
The present invention was made in order to solve the above-mentioned problems, and an object of the invention is to provide a metal gasket for a cylinder head gasket and so on, constituted by multiple plates, wherein a first metal substrate includes a main full bead in the sealing hole, and a second metal substrate to be laminated on a depression side of the main full bead includes binding beads which bind the expansion of bottom portions at a portion where the bottom portions of the main full bead abut. The deformation of a widening direction of the bottom portions of the main full bead is bound or limited by the binding beads of the second metal substrate so that appropriate bead stiffness can be obtained. Accordingly, the metal gasket can distribute and maintain an appropriate surface pressure around the cylinder bore, and obtain an excellent sealing performance.
Further objects and advantages of the invention will be apparent from the following description of the invention.